In soil, some specific bacterial populations, called plant growth-promoting rhizobacteria are able to promote plant growth and/or reduce the incidence of soil-borne diseases. Rhizosphere competence is an important prerequisite for the efficacy of these biocontrol strains. Therefore, over decades, multiple approaches have been combined to understand the molecular basis of bacterial traits involved in rhizosphere competence. This review addresses the bacterial genes expressed during bacterial–plant interactions in the rhizosphere of different plant species. The distribution of these key genes in natural populations of rhizobacteria is also discussed.